Fas idle....1200 rpm 14,4 volts 100 amp alternatorHF 500 amp carbon pile load tester connected to battery.Using logical thinking only,........If I gradually load the system, at what amperage should should the voltage start to drop dramatically ?In other words, should it hold the +14 volts at an 80 amp load ?And that would indicate a good alternator ?Any tech help on this apprecieated

Chances are that the voltage at the alternator output will be about 1 volt higher than the battery voltage where the load tester would be connected under a 100 amp load. THis is due to the #8 wire running between most alternators and the battery. The small wire will prevent alternator overloads - I guess?So how to put a 100 amp load on a battery with a 500 amp load tester? Can you divide the load up into 100 or 50 amp sections, and only put that load on the battery?I would expect the voltage to drop into the 13.8 volt range at 100 amps load on it. Just because of the voltage loss across the internal diodes within the alternator. Also as the alternator warms up, most manufactures claim that they will only put out about 80% of their cold rating. Yes you already realize that many require at least 2,000 alternator RPM to put out anything near the rated amperage.Fred.

Step one: Go to local auto parts store and have them test the altenatorStep Two: Go back home and install the altenator

I'd be a little careful putting a long term heavy load on an alternator. I suspect the 100 amp rating is not a continuous rating. Maybe not even close to that.

Adjusting for specific load no problem w/ the carbon pile tester.I know the 100 amp load is for short term testing, as it heats stuff up perdy fast.Auto Parts testing ?? Anybody can do that,....besides that the nator is not off the vehicle.Thanks for the tips. I think I will load it at 80 amps for 10 seconds, and expect it to hold 13.5+, and if so, I'll call it good.Is it possible to show 14+ volts, but be drastically short on amperage ?? I'd guess maybe it is.

I don't think any alternator will put out near rated current at fast idle, I think you will be lucky to get 40 amps at that speed.

How to Load test an alternator ? | Good Sam Community

Golden_HVAC
Explorer
Jun 17, 2014
Chances are that the voltage at the alternator output will be about 1 volt higher than the battery voltage where the load tester would be connected under a 100 amp load. THis is due to the #8 wire running between most alternators and the battery. The small wire will prevent alternator overloads - I guess?

So how to put a 100 amp load on a battery with a 500 amp load tester? Can you divide the load up into 100 or 50 amp sections, and only put that load on the battery?

I would expect the voltage to drop into the 13.8 volt range at 100 amps load on it. Just because of the voltage loss across the internal diodes within the alternator. Also as the alternator warms up, most manufactures claim that they will only put out about 80% of their cold rating. Yes you already realize that many require at least 2,000 alternator RPM to put out anything near the rated amperage.

Fred.

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How to Load test an alternator ?

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